Bump tornado from 6.4 to 6.4.2 in /docs

Bumps [tornado](https://github.com/tornadoweb/tornado) from 6.4 to 6.4.2.
- [Changelog](https://github.com/tornadoweb/tornado/blob/v6.4.2/docs/releases.rst)
- [Commits](tornadoweb/tornado@v6.4.0...v6.4.2)

---
updated-dependencies:
- dependency-name: tornado
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

docs/requirements.txt

@@ -155,7 +155,7 @@ tinycss2==1.2.1 ; python_version >= "3.9" and python_version < "3.13"
 toml==0.10.2 ; python_version >= "3.9" and python_version < "3.13"
 tomli==2.0.1 ; python_version >= "3.9" and python_version < "3.11"
 tomlkit==0.12.3 ; python_version >= "3.9" and python_version < "3.13"
-tornado==6.4 ; python_version >= "3.9" and python_version < "3.13"
+tornado==6.4.2 ; python_version >= "3.9" and python_version < "3.13"
 tqdm==4.66.1 ; python_version >= "3.9" and python_version < "3.13"
 traitlets==5.14.1 ; python_version >= "3.9" and python_version < "3.13"
 typed-ast==1.5.5 ; python_version >= "3.9" and python_version < "3.13"